Aerosol is a form of packing in which a gas under pressure, or a liquified gas which has a pressure greater than atmospheric pressure at ordinary temperatures, is used to spray a liquid. The result of spraying is to produce a mist of small liquid droplets in air. Numerous products such as paints, air fresheners, deodorizers, insecticides, waxes, cleaners, personal care products--shaving creams, deodorants, etc. are dispensed with aerosols. A typical aerosol package is a sealed unit to avoid leakage. The vapor phase consists primarily of the propellant, whereas the liquid phase is propellant dissolved in active ingredients. The contents of an aerosol contain surface active agents, stabilizers and solvents. Aerosols usually operate at pressures between 30-50 psig and may contain as much as 90% propellant.
Chlorofluorocarbons and liquified petroleum gases are two types of chemicals popular for use as aerosol propellants. In the refining of crude oil, the overheads product mainly contains mixed butanes, which can through distillation produce suitable "cuts" for the propellant industry. A typical LPG propellant will mainly contain isobutane and butane, with small amounts of propane.
The main source of propellants is the petroleum refineries and natural gas processing plants. Often the butanes are catalytically isomerized to produce isobutane. There are always traces of sulfur and other compounds that make the direct use of butanes impossible, without further treatment. These trace contaminants are removed by various means. U.S. Pat. No. 4,108,916 has revealed a method for eliminating unsaturated hydrocarbons by treating with concentrated sulfuric acid. U.S. Pat. Nos. 4,351,980; 4,425,226 and 4,491,563 have discussed the use of transition metals and clays for deodorizing through various means.
The technical literature attributes odor to a variety of chemical species such as unsaturates, ketones, alcohols, etc. Although the boiling points of the odor causing four carbon atom compounds are far enough apart, separation by distillation is not economically feasible, rarely required, and sometimes not possible.
Through various contamination processes, oxygen and oxygenated compounds are formed in butanes. One mechanism by which oxygen is introduced into the system is through walls of the pressure vessel used to transport butane. When empty or during inspections the walls of the pressure vessels are exposed to atmospheric oxygen. The surface is coated with rust, which gradually releases oxygen. Also during transfer operations, line filled oxygen ends up in the butane.
Oxygen in the presence of naturally occurring catalyst like, iron form a series of compounds like acetone, tertiary butyl hydroperoxide, methanol and isobutylene. Most of oxygenated products have a characteristic odor and are soluble in water.
It is this water soluble property that is used in the present invention to deodorize liquified petroleum gases.
Although there is abundance of butanes, only the preferred feedstocks meet rigid requirements of personal care products industry. And a high price is paid for odor free aerosol propellants. The present disclosure provides a process and a preferred embodiment to refine LPG gases and upgrade them.